We recently identified Kr|pple-like factor 7 (KLF17) as a negative regulator of epithelial-mesenchymal transition (EMT) using a genome-wide RNAi screen in mice. The human KLF17 gene is located at chromosome 1p34 where allelic loss of heterozygosity (LOH) correlates with poor prognosis in breast cancer. The overall goal of this proposal is to determine the molecular mechanisms and genetic regulation of transcription factor KLF17 in tumor maintenance and EMT, and determine the therapeutic value of KLF17 modulation and prognostic value of KLF17 in breast cancer. We will use molecular profiling, cellular assays and animal models to elucidate the mechanisms of KLF17 functions and regulation. We will proceed from the following aims: Aim 1. Determine the molecular mechanisms of KLF17 regulation and function in tumor growth and EMT. We will determine the effect of Id2 and ARHGAP29, regulated by KLF17, individually and the combined effect of these two genes on tumor cell growth and EMT both in vitro and in mouse models. We will use in vitro assays and in vivo orthotopic transplantation mouse models to test their functions in tumor invasion and metastasis. Epistasis analysis will be performed to determine whether these genes are major mediators of KLF17 in tumor growth and EMT. We will also investigate the molecular mechanisms of KLF17 regulation by SNAI1 (Snail), a known EMT regulator, transcriptionally and by microRNA miR-129 post-transcriptionally. We will determine whether KLF17 is a direct target of SNAI1 and whether miR-129 directly targets KLF17 at its 3'UTR. The functions of SNAI1 and miR-129 in EMT and tumor invasion will be determined by in vitro assays and tumor xenograft mouse models. Epistasis analysis will be performed to determine whether KLF17 is a major mediator of SNAI1 and miR-129 in EMT and tumor invasion. Aim 2. Characterize the function of KLF17 in tumor maintenance. We will use xenograft models and cells expressing KLF17 short hairpin RNA (shRNA) and Ras in an inducible vector to test whether modulation of KLF17 expression alone or in combination with Ras inhibition can cause tumor regression in breast cancer. We will investigate whether KLF17 knockdown antagonizes Ras-induced senescence in tumors using xenograft animal models and determine the pathways that KLF17 interferes with in Ras-induced senescence. These experiments will determine whether KLF17 alone or in combination with Ras can serve as a potential therapeutic target in the treatment of breast cancer. Aim 3. Determine the prognostic value of KLF17, Id1, SNAI1 and miR-129 in clinical breast cancer samples. We will determine the expression of KLF17 and Id1, along with Snail and miR-129 in clinical primary breast cancer samples with known clinical outcomes to assess whether they can be used as prognostic markers for relapse in breast cancer.